The present invention relates generally to screens utilized in subterranean wells and, in an embodiment described herein, more particularly provides apparatus for inspecting well screens and associated methods of inspecting well screens.
A typical well screen is generally tubular in shape and may be on the order of twenty or thirty feet in length. Very basically, the typical well screen includes a generally tubular filtering portion attached in an overlying relationship to a perforated tubular base pipe. The filtering portion operates to exclude sand and other particulate matter from entering a string of production tubing extending to the earth's surface. The base pipe facilitates interconnection of the well screen to the tubing string.
A variety of representative configurations of well screens may be found in a publication entitled HALLIBURTON SCREENS, published by Halliburton Energy Services of Duncan, Okla. The disclosure of this publication is incorporated herein by this reference. Therein it may be seen that well screen configurations include filtering portions which have a single wire wrapped jacket, multiple concentric wire wrapped jackets with gravel or graded sand between the jackets and a sintered metal sleeve. Wire wrapped jackets generally include a series of circumferentially spaced apart and longitudinally extending ribs, with a triangular or keystone-shaped wire helically wrapped about the ribs.
In use, it is important that the filtering portion of a well screen exclude sand or other particles from fluid flowing through the filtering portion. The filtering portion is manufactured to exclude a certain specified minimum size of particle, with the specified size varying depending upon the application. If particles larger than the specified size are not excluded by the filtering portion, they will enter the production tubing and may cause significant damage and economic loss during operation of the well. However, if the filtering portion is made to exclude too small a size particle, fluid flow therethrough will also be impeded and the filtering portion may easily become clogged with fine particles, reducing the rate of production from the well.
To prevent such damage and other economic loss, well screen manufacturers inspect their well screen filtering portions. Usually, this inspection is performed before the filtering portion is attached to the base pipe. Unfortunately, prior to the present invention, these inspections have been somewhat unreliable.
In one method of inspecting a wire wrapped jacket, a thickness gauge is inserted between adjacent wraps of wire to determine whether the wire wraps are properly spaced apart. If the wraps are spaced too far apart, large particles will be permitted to flow between the wraps. If the wraps are spaced too close together, a large resistance to fluid flow therethrough will result. It is, however, impractical to insert a thickness gauge between all wraps of a long well screen. Therefore, these insertions are typically done only at several selected places, leaving a significant part of the filtering portion essentially not inspected.
Another inspection technique, which is particularly useful with a filtering portion having multiple wire wrapped jackets and gravel therebetween (hereinafter referred to as a "prepacked" jacket), is to insert a light bulb within the filtering portion and look for excessive light passed through the prepacked jacket. Such excessive light may indicate that the inner and outer wire wrapped jackets are not concentric (thereby producing a thin layer of gravel therebetween on one side), the gravel is not tightly packed therebetween, the wire wraps on one or both of the wire wrapped jackets are too far apart, etc. Unfortunately, this method relies on the subjective determination of the person viewing the light and provides no quantitative basis on which to establish criteria for accepting or rejecting a particular filtering portion.
Additionally, neither of the above methods produces data which may be utilized to indicate a resistance to flow of fluid through the filtering portion. An indication of hydraulic resistance of the filtering portion would be useful in enabling a well operator to choose a well screen suited for desired particular flow characteristics of a well. Thus, the well operator would be given more control over the production and/or long term performance of the well.
From the foregoing, it can be seen that it would be quite desirable to provide a method of inspecting well screens which does not rely on spot checks of the filtering portion, and which does not rely on subjective determinations, but which permits filtering portions to be accurately and conveniently inspected. In addition, it would be desirable to produce an indication of the hydraulic resistance of a filtering portion as a result of the inspection. It is accordingly an object of the present invention to provide such a method and associated inspection apparatus.